Learn how pool and landscape designers use natural stone, artificial rock, or a combination to create waterfalls, retaining walls, caves, grottos, and pools.
Using Natural Stone & Artificial Rock in Swimming Pool Designs
By Elissa Sard Pollack
Whether they use natural stone, simulated rock or a combination, talented pool and landscape designers create lagoon-style marvels that rival Mother Nature. Caves, grottos and waterfalls are just a few of the rocky creations that transform basic backyard pools into crystal clear ponds that appear to be carved from their surroundings.
Natural boulders can function as simple landscape accents, too. A few small stones placed strategically along a pathway, in a planting bed, on the pool deck, or even within the pool, can help unify the design. At the other end of the scale, two-ton boulders can form a 10-ft. high waterfall. In-between, the options include diving rocks incorporated into stone walls or boulder waterfalls, a treatment standing alone on the water's edge, an island tanning platform, or a spillway from an elevated spa or upper pool into a lower pool. Rock can also form retaining walls or underwater bands that signal elevation or depth changes, as well as caves, slides or handrails cut from limestone.
The only limit on the scope of a rock creation is your budget. One monetary concern is the source of the rock. Rock may be mined and shipped, or it can be unearthed during the excavation process. When the perfect rocks are found on site, the shipping costs are eliminated; however, one should not count on such a discovery. On two adjacent properties in Texas Hill Country, for example, it is not uncommon for one crew to excavate limestone boulders the size of a car, and right next door find only baseball size stones after three weeks of digging. Either scenario can result in a masterful waterfall combining limestone of various sizes, colors and textures.
Another common choice for waterfalls in parts of Texas is moss rock, which is shipped to other regions as well. Moss rock gets its name from the dry lichens attached to it, which give it a gray or green hue. Meanwhile, stacked flagstone is a typical choice for a fireplace or retaining wall, and tumbled flagstone may line a meandering stream.
While some builders are fortunate enough to work in environments rich with usable stone, others routinely import Rocky Mountain quartz, Tennessee crab orchard stone and Pennsylvania bluestone or limestone. Greater shipping distances can drive up the cost of your stone water feature.
Choosing the Right Type of Stone
While budget may be a factor in setting the scale of the project, once you select certain elements, the rock choice depends primarily on the desired color, and, secondarily, on what is being created from the rock. Therefore, a diving platform should have a large, smooth surface that will be safe and comfortable for bare feet. Also, flat slabs stack well for retaining walls and work as coping, while large round boulders are best for building giant waterfalls and to retain ground in significant grade change applications. Furthermore, white limestone behaves like a naturally cool deck, whereas dark brown Oklahoma stone may get too hot in the sun for walking comfortably.
As important as these kinds of selections are, the stone's color is often the deciding factor--but be careful. One might think that Pennsylvania bluestone would have a consistent bluish tint; however, it can be different shades of green, gray, brown, and, yes, sometimes blue. Because of the wide variety available, many builders bring their clients to the stone yard to select the stone that will best complement the architecture of the home and other plans for the property.
Most builders of the kind of high-end pools that would incorporate this fine rockwork put desired color and texture at the top of the list and workability at the bottom, assuming the budget can cover the selection.
Another approach is using faux rock in your pool design, so you get exactly the color and texture you want. Various processes can be used to sculpt rock on site. Some companies use a series of panels made from castings of natural rock formations that can be combined to create nature-mimicking scenes—from small outcroppings to 27-ft. long waterslides.
Another method starts with a welded steel frame that is shot with gunite, sculpted, and then stamped to create the desired texture. Handcarved cracks and striations help such products mimic nature, making your artificial rock waterfall look authentic. A similar process can be used to add fake trees to a setting. Concrete "trees" will never die, and acid stained concrete "rock" will never fade or shift, proponents argue. These materials can even survive hurricanes and hold up well in the freeze-thaw cycles of northern climates.
Devotees of faux rock would rather design to the exact desires of the client than haul in heavy boulders with cranes. They also prefer forming and attaching manmade rocks to a raised beam over setting large boulders in place. Manmade products may work well in large-scale projects because they are far lighter than natural boulders.
Combining Natural Stone and Faux Rock
While many pool builders and landscape architects use either natural stone or manmade rock, some combine the two approaches. For instance, if the inside of a grotto contains manmade stone, the placement of interior fiber-optic lights can mimic constellations, and natural boulders can form the exterior.
Additionally, one might incorporate natural stacked stone in retaining walls because it is attractive and manageable, while using poured concrete "boulders" on a wall with a vanishing edge because of the structural advantages of pouring concrete over attempting to anchor a large heavy stone.
Creating an authentic looking poolscape is important, particularly when blending natural and manmade materials. Even projects that rely almost entirely on natural boulders for their aesthetics will often have a concrete deck and a plaster pool. Keep in mind that darker interior finishes, such as colored plaster or a pebble or quartz finish, are more reflective, and they can enhance the authenticity of a natural pond look. Lighter colors replicate a sandy shore. Textured decking treatments, like stamped or brushed concrete, can also give natural stone designs geological realism.
With the right combination of material and craftsmanship, your backyard can conjure up a sandstone desert oasis, a rocky mountain stream or a secluded swimming alcove on a Caribbean island.
Photo courtesy of Aquatic Artists, Inc., Youngsville, NC